Mechanical lock

1. A mechanical lock, comprising an outer tube and a linear arrangement of interlinked components arranged in a core of the outer tube, the interlinked components comprising at least three coaxially arranged, separately manufactured, elements, including a central tie and two link-rods, the two link rods being respectively interlinked at first ends thereof to opposing ends of the central tie by expandable components.

2. A mechanical lock according to claim 1 , wherein the expandable components each comprise a plurality of elements that are expandable away from one another.

3. A mechanical lock according to claim 2 , wherein the expandable components are fingers of a collet-like arrangement.

4. A mechanical lock according to claim 1 , wherein the link rods extend, at their opposite ends, out of the outer tube.

5. A mechanical lock according to claim 1 , wherein the link rods extend, at their opposite ends, to respective brackets of an actuator mechanism for a railway points arrangement.

6. A mechanical lock according to claim 1 , wherein the outer tube is mounted, in use, in a fixed position relative to a frame of an actuator mechanism for a railway points arrangement, or relative to the ground, or relative to a nearby sleeper.

7. A mechanical lock according to claim 1 , wherein the link-rods have rod ends for engaging internally of the expandable components.

8. A mechanical lock according to claim 1 , wherein the internal surface of the outer tube is smooth walled.

9. A mechanical lock according to claim 1 , wherein there are no grooves or recesses in the internal surface of the outer tube into which elements of the expandable components can engage or lock.

10. A mechanical lock according to claim 1 , wherein each expandable component is adapted to interface with the respective end of the respective link-rod via a tapering surface.

11. A mechanical lock according to claim 1 , wherein the interference between the end of each rod and the respective expandable component is such that a pushing of the rod towards its respective expandable component causes the expandable component to expand for bearing against the internal wall of the outer tube.

12. A mechanical lock according to claim 1 , wherein the expandable components are each formed as collets, comprising a plurality of fingers.

13. A mechanical lock according to claim 1 , wherein the expandable components are each formed of a plurality of separable components.

14. A mechanical lock according to claim 13 , wherein the separable components are a plurality of fingers connected together by one or more circlip, snap-ring or ring of wire.

15. A mechanical lock according to claim 1 , wherein the expandable components each comprise a plurality of fingers that are uniformly spaced around the ends of the respective link-rods or around the ends of the opposing ends of the central tie.

16. A mechanical lock according to claim 1 , wherein the expandable components each have a tapering outer surface.

17. A mechanical lock according to claim 16 , wherein the taper is a dual taper, such that the outer surfaces of the expandable components each define a distal taper that reduces towards the distal end thereof and a proximal taper that reduces towards the proximal end thereof.

18. A mechanical lock according to claim 1 , wherein the outer tube has a cylindrical internal wall along its whole length.

19. A mechanical lock according to claim 1 , wherein outer surfaces of the expandable components define in transverse cross section, segments of a circle having a diameter substantially corresponding to, or slightly less than, the internal diameter of the outer tube.

20. A mechanical lock according to claim 1 , wherein the link rods and the central tie have generally circular, cylindrical or annular cross sections along at least a substantial part of their lengths.

21. A mechanical lock according to claim 1 , wherein the elements of the expandable components define individual frustrated segments of a circular or cylindrical cross section, such that collectively they define an annular, or substantially annular, cross section.

22. A mechanical lock according to claim 1 , wherein the rod ends engaged within the expandable components have a tapered outer surface.

23. A mechanical lock according to claim 1 , wherein the expandable components each have a tapered inter surface having a reducing dimension relative to the axis of the lock as the taper leads towards the axial centre of the central tie.

24. A mechanical lock according to claim 1 , wherein the mechanical lock substantially has a rotational symmetry about its longitudinal axis.

25. A mechanical lock according to claim 1 , wherein the mechanical lock is substantially symmetrical about a transverse plane extending through the axial center of the central tie.

26. A mechanical lock according to claim 1 , wherein the ends of the rod are provided as separable components from a shaft of the rod.

27. An actuator mechanism for a railway points arrangement fitted with at least one mechanical lock for locking switch rails in a desired position, the mechanical lock being in accordance with claim 1 , and the outer tube thereof being mounted in a fixed position relative to a frame of the actuator mechanism.

28. An actuator mechanism of claim 27 , wherein the actuator mechanism comprises a pair of hydraulic rams, each ram having a base component that is mounted in a fixed position relative to the frame of the actuator mechanism.

29. A railway points arrangement comprising a pair of stock rails, a pair of switch rails and an actuator mechanism according to claim 28 , the mechanical lock thereof being a mechanism for locking one of the switch rails against its respective stock rail, the mechanical lock being arranged such that it extends substantially between the two switch rails, between two brackets of the actuator mechanism.

30. A method for selectively locking the position of a pair of switch rails relative to a pair of stock rails comprising providing an actuator mechanism with a mechanical lock according to claim 1 and arranging the mechanical lock to extend between the two switch rails, linking each link-rod of the mechanical lock to one of the switch rails via a bracket of the actuator mechanism, and mounting the outer tube of the mechanical lock in a fixed position relative to a frame of the actuator mechanism, or relative to the ground, or relative to a nearby sleeper upon which the stock rails are fixedly mounted.

31. A method for selectively locking the position of a pair of switch rails relative to a pair of stock rails comprising providing an actuator mechanism with a mechanical lock according to claim 29 and arranging the mechanical lock to extend between the two switch rails, linking each link-rod of the mechanical lock to one of the switch rails via a bracket of the actuator mechanism, and mounting the outer tube of the mechanical lock in a fixed position relative to a frame of the actuator mechanism, or relative to the ground, or relative to a nearby sleeper upon which the stock rails are fixedly mounted.